The field of the invention relates generally to electric motors, and more specifically, to a motor controller, a drive circuit, and methods for combined electric motor control.
Motor drive systems used in air-conditioners and heat pumps of heating, ventilation, air-conditioning (HVAC) applications typically utilize an active power factor correction (PFC) AC-DC stage and use large aluminum electrolytic capacitors (e.g., 3000 microfarads), in order to maintain constant DC voltage, increased power factor, reduced harmonics, and longer lifetime of electrolytic capacitors. As a result, such systems have lower power density, lower efficiency and higher cost. Additionally, a large DC-link capacitance leads to high inrush current during the power-up process. A relay or multiple-relays may be used to control the inrush current, which further increases the system size, cost, and the burden of auxiliary lower power supply design. Moreover, in some applications, ground-fault protection must be included in HVAC products, which typically involves multiple sensors and/or expensive common-mode current transformers to detect ground fault currents.
Stand-alone low-capacitance motor drive systems (also referred to as direct power transfer (DPT) technology) have been developed in lower power (i.e., less than or equal to 1 HP) HVAC air-moving applications. This DPT technology uses a film capacitor (i.e., less than 10 uF) as the DC-link energy storage component. The film capacitor significantly reduces the inrush current, eliminates the bulky DC-link electrolytic capacitors and the corresponding reliability concern, and offers the feasibility of packaging the overall motor drive system. However, DPT technology includes certain other design challenges, such as lightning protection concerns and larger voltage regeneration.